As the minimum line widths of elements integrated into a semiconductor chip and connection wires thereof are reduced, it is difficult to avoid an optical proximity effect (OPE) of patterns formed on a wafer by means of a conventional lithography technique using ultraviolet rays. Since the wavelength of an I-beam, which is one recently used ultraviolet rays, is 0.365 μm, while the minimum critical dimension of the line width is 0.35 μm, the OPE of the patterns due to diffraction and interference of light severely limits a fabrication process of the semiconductor chip. It is estimated that the OPE of the patterns becomes severer so as to meet the reduction in the minimum critical dimension of the line width. Accordingly, optical proximity correction (OPC), which corrects the OPE generated in resolution limit in photolithography, is inevitably performed.
In photolithography, patterns of the photo mask are reproduced onto a wafer through an optical lens. Here, an optical system projecting images serves as a low-pass filter, and an image formed on the wafer has a distorted shape. Where a photo mask having a rectangular shape is used, portions having a high frequency, i.e., edge portions, do not permeate the optical lens, thereby forming a circular-shaped pattern on the wafer. In the case that the pattern of the photo mask has a large size (or cycle), since the basic space frequency is low, comparatively high-ordered frequencies can permeate the optical lens, thereby forming a pattern on the wafer similar to the pattern of the photo mask. However, in the case where the pattern of the photo mask has a small size, since the space frequency is high, the frequency permeating the optical lens is reduced, thereby causing the distortion of the pattern to become severe.
Accordingly, until now, the above problems have been resolved by development of photolithography equipment. However, the development of this equipment is limited, and approaches in an aspect of the design field are now needed. In the OPC of the patterns of the photo mask, the patterns of the photo mask are deformed in advance in consideration of the above distortion so that final patterns formed on a wafer have the desired shape. Generally, OPC employs a rule-based method, in which several rules are made and are reflected in designing the patterns.
FIG. 1 is a flow chart schematically illustrating a conventional process for testing database patterns of a photo mask.
As shown in FIG. 1, in the conventional process, a rule file regarding line critical dimensions (CD) or spaces of designed database patterns are made, design rule check (DRC) of the rule file is performed, and then optical proximity correction (OPC), in which the shapes of the database patterns are deformed so that the final patterns exposed on a wafer have the desired shapes, is formed (S10˜S30).
In the conventional process for testing database patterns of the photo mask, the line CDs or the spaces of the patterns are tested in the DRC, but failure of the patterns due to failure in a patterning step is not detected. In the patterns of the same critical dimension, it is impossible to distinguishably test a pattern having a long line length and a pattern having a short line length. Accordingly, in the case that the pattern having a long line length, which was corrected by the OPC, is exposed onto the wafer, the patterns collapse or a bridge is formed between the neighboring patterns.